A good thing about Bear Mountain is that millions of people can get to it. A bad thing is that millions of people can get to it. So over the years, the trails have been rebuilt and relocated many times. By the 1990s, it was clear that the Bear Mountain section of the trail, used by a half-million people a year, needed to be rebuilt again. The solution, drawn up primarily by Mr. Walsh and another trail designer, Peter Jensen, was an impossibly ambitious series of steps and walkways supported by native stone.

It would last, one hoped, forever. It would keep neophytes on the trail instead of bounding out into the woods. It would work for urban hikers showing up in tennis shoes and flip-flops, as well as for serious long-haul hikers. And it would be a challenge to build.